Nonmonotonic Angle-Dependent Friction on Twisted Bilayer Graphene

Moiré superstructures in stacked two-dimensional (2D) materials offer a promising means for tailoring tribological properties, yet the experimental dependence of friction on continuously varying moiré patterns remains unexplored. Here, we systematically investigate the frictional response of twisted bilayer graphene (TBG) across twist angles from 0.3° to 10.8°. Both lateral force modulation amplitude and frictional dissipation exhibit nonmonotonic variations. For lateral force amplitude, it peaks at ∼3.0°, validating the prior predictions based on the geometric interplay. In contrast, frictional energy dissipation reaches its extremum at a notably smaller twist angle of ∼1.2°. This distinct nonmonotonic trend is attributed to the competition between the local in-plane stiffness and its atomic reconstruction state, both of which influence the onset of unstable moiré-scale slip. Our results highlight the critical role of local in-plane stiffness of superstructures in governing sliding dynamics and energy dissipation, offering insights into moiré engineering for controlling surface friction.